Conversion Factors, SI Units

The pilot will perform a number of calculations during preflight planning and the one we used on the site are listed below for convenient access. Sometimes the use of a special aviation calculator (E6B models or electronic Jeppesen) is required.

Previous article discussed the formula's used in aviation calculations but sometimes we need to convert between different systems be that volumes, densities or mass. The table below shows some of the common ones used. For common fuel conversion see the image to the right. We also provide the most commonly used prefixes that are used with these base units.

Conversion tables

Using these conversions is quite simple. For example: to convert 150 US gal to liters is 150 x 3.785 = 567.75 liters. If you want to convert from liters to US gal then divide the number of liters by the conversion factor.

Volume, SI unit cubic meter (m3)

Convert from:

To:

Multiply by:

m3

ft3

35.315

in3

cm3

16.387

US Gal

liters

3.785

UK Gal (Imperial)

liters

4.546

US Gal

m3

3.785 x 10-3

UK Gal (Imperial)

m3

4.546 x 10-3

Mass (Weight), SI unit kilogram (kg)

Convert from:

To:

Multiply by:

kg

lb

2.2046

lb

g

4.536 x 102

Pressure, SI unit Newton/square meter (N/m2)

Convert from:

To:

Multiply by:

N/m2 (pa)

bar

10-5

lbf/in2 (psi)

N/m2 (pa)

6.895 x 103

lbf/in2

hPa (mbar)

68.948

kgf/cm2

N/m

9.807 x 104

inHg

hPa (mbar)

33.864

Bar

Pa (N/m2)

105

Energy / Power / Heat flow SI unit Watt (W)

Convert from:

To:

Multiply by:

hp

kW

0.7457

ft.lbf/s

W

1.3558

Btu/hr

W

0.2931

kWh

MJ

3.6

cal

J

4.1868

Btu

kJ

1.055

Btu

kWh

2.9307 x 10-4

Prefixes

Sometimes I see these prefixes not being used in the correct way. For example: the use of the kilo prefix is being mistakenly written as K (which is Kelvin) where it should be k (lower case). The table below shows them with their factor.

Commonly used Metric prefixes with SI base units

Prefix

Symbol

Factor

Yotta

Y

1024

Zeta

Z

1021

Exa

E

1018

Peta

P

1015

Tera

T

1012

Giga

G

109

Mega

M

106

kilo

k

103

hecto

h

102

deca

da

101

deci

d

10-1

centi

c

10-2

milli

m

10-3

micro

μ

10-6

nano

n

10-9

pico

p

10-12

femto

f

10-15

atto

a

10-18

zepto

z

10-21

yocto

y

10-24

More commonly used conversions can be found on websites like onlineconversion.com and wikipedia.